An adaptor for a window locking mechanism wherein the locking mechanism includes a keeper on a window sash and a cam roller on a window frame, the adaptor comprising a body portion having first and second sides with a recess being formed in the body portion, the recess being sized to receive a portion of the cam roller, the body portion further having at least one ramped portion extending from an edge of the recess to the first side. The adaptor can be used with conventional cam roller windows and provides an improved surface engagement and a greater displacement span.